On February 17, 2026, the U.S. government released new intelligence alleging that China conducted a secret underground nuclear test at its Lop Nur test site in June 2020, reigniting global debates over nuclear proliferation and raising concerns about a renewed arms race. The revelation, shared by Christopher Yeaw, Assistant Secretary for Arms Control and Nonproliferation at the State Department, has stirred controversy among international monitors, scientists, and diplomats, with China issuing a categorical denial and independent experts urging caution over the evidence.
The seismic event at the center of the controversy was detected on June 22, 2020, by a remote station in Kazakhstan, roughly 450 miles from Lop Nur in western China. According to Yeaw, the event registered a magnitude of 2.75 and was, in his words, "very likely a nuclear explosive test." At a Hudson Institute event in Washington, Yeaw emphasized, "There is very little possibility that it is anything other than an explosion, a singular explosion. It is quite consistent with what you would expect from a nuclear explosive test." He further clarified that the data was not consistent with mining activity or a natural earthquake, and he asserted, "It’s also entirely not consistent with an earthquake."
Yet, the seismic data is far from conclusive. The Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO), which operates a global network of monitoring stations, confirmed that its PS23 station in Kazakhstan recorded "two very small seismic events, 12 seconds apart" on that day. However, as CTBTO Executive Secretary Robert Floyd stated, "With this data alone, it is not possible to assess the cause of these events with confidence." The events were well below the threshold—about 500 metric tons of TNT—at which the CTBTO can reliably identify nuclear explosions. Ben Dando, head of seismology and verification at NORSAR, a Norwegian organization specializing in nuclear test monitoring, echoed this skepticism, telling NPR, "I would not say that there's really strong conclusive evidence. We can't really confirm or deny whether a nuclear test took place at this point."
China's response was swift and unequivocal. During a press conference, Foreign Ministry spokesperson Lin Jian dismissed the allegations as "completely groundless," while the Chinese embassy in Washington went further, accusing the U.S. of "political manipulation aimed at pursuing nuclear hegemony and evading its own nuclear disarmament responsibilities." Embassy spokesperson Liu Pengyu insisted, "This is political manipulation aimed at pursuing nuclear hegemony and evading its own nuclear disarmament responsibilities." China, which signed but has not ratified the 1996 Comprehensive Nuclear-Test-Ban Treaty, maintains that it has abided by the test ban since its last official underground test in 1996. "China urges the U.S. to reaffirm the five nuclear-weapon states' commitment on refraining from nuclear tests, uphold the global consensus against nuclear tests, and take concrete steps to safeguard the international nuclear disarmament and non-proliferation regime," Liu stated.
The U.S. itself is in a complex position. Like China, it has signed but not ratified the test ban treaty. Its last underground nuclear test took place in 1992. Since then, the U.S. has relied on a multibillion-dollar program of supercomputer simulations and non-nuclear experiments—sub-critical tests—to ensure the reliability of its nuclear arsenal. In 2024, NPR reporters were granted rare access to some of the tunnels where these sub-critical tests occur, witnessing firsthand the lengths to which the U.S. goes to maintain its arsenal without crossing the nuclear test threshold.
Meanwhile, China has been busy at Lop Nur. According to Tong Zhao, a senior fellow at the Carnegie Endowment for International Peace, satellite imagery has revealed significant expansion at the site in recent years, including new tunnels, expanded equipment areas, and additional housing for personnel. "It looks like China is investing significantly into maintaining, if not expanding, the missions at the testing site," Zhao noted. The Pentagon estimates that China's nuclear arsenal has grown rapidly, from about 200 warheads in 2019 to more than 600 today, with a goal of exceeding 1,000 by 2030. This expansion is viewed with concern in Washington, where officials worry that China is seeking not just parity but strategic advantage.
Yeaw and other U.S. officials have alleged that China may have attempted to conceal the true size of the 2020 explosion by using "decoupling" techniques—detonating the device in a large underground cavity to muffle the seismic signature. "We do know that nations don't take these risks … without an expectation of significant gain," Yeaw said. If decoupling was used, the actual yield of the test could have been much larger than the seismic readings suggest—potentially in the hundreds of tons or even up to a kiloton of TNT equivalent. Dando explained that while a magnitude 2.75 event would normally correspond to an explosion of tens of tons of TNT, decoupling could mask a much larger blast.
Why would China risk conducting such a test? According to Zhao, the motivations could range from developing lower-yield nuclear weapons suitable for limited conflict scenarios to testing new warhead designs for hypersonic delivery systems. The U.S. has conducted more than a thousand nuclear tests since 1945, while China has carried out only 45, giving Chinese scientists a strong incentive to gather more data as they expand their arsenal. U.S. Undersecretary of State for Arms Control and International Security Thomas DiNanno recently claimed that China was "skirting the line with the test moratorium" and preparing for larger-yield tests in the future.
The timing of these revelations is significant. The New START treaty, the last remaining arms limitation agreement between the U.S. and Russia, expired on February 5, 2026, fueling anxieties about a new era of unconstrained nuclear competition. President Donald Trump has used the allegations about China as a catalyst to push for the resumption of U.S. nuclear testing, arguing that America must act "on an equal basis" with its rivals. The administration is also urging China to join trilateral arms control negotiations with the U.S. and Russia, though Beijing has so far resisted, arguing that its arsenal is dwarfed by those of Washington and Moscow.
Independent experts are urging caution, warning that a return to nuclear testing could accelerate a global arms race and undermine decades of progress toward non-proliferation. Some note that the U.S., with its vast experience and advanced simulation capabilities, may have less to gain from new tests than China, whose scientists would benefit disproportionately from even a small number of additional explosions.
As the debate intensifies, the world is left to grapple with uncertainty. The evidence for a Chinese nuclear test in 2020 remains contested, yet the geopolitical consequences are already reverberating. With both superpowers modernizing and expanding their arsenals, and the international arms control architecture under strain, the stakes for global security have rarely felt higher.
The U.S. government’s allegations have cracked open a new chapter in the nuclear age—one marked by suspicion, technological rivalry, and the uneasy specter of resumed testing. Whether this leads to fresh negotiations or a dangerous escalation may depend less on what happened beneath the sands of Lop Nur, and more on what the world’s leaders choose to do next.